heart is breaking

No, you are not being foolish and if it helps you to keep writing, do it. Even if you feel they will just throw the letters away, you've kept the faith and continued to say how much you love them.
Try not to make any comments about their father though; just general chit-chat and pleasant day-to-day stuff.

One day they WILL listen to their Mom, they'll find out the truth, I'm sure of it.

Live up to your name there is always hope.

I m not sure I understand this if they ve joined the military they are both adults
You were estranged from your daughter because of the controlling husband but you had a loving relationship with the two grandsons and took them everywhere So he didn’t control their childhood relationship with you ? but now they are adults he’s poisoned them against you ?
Sorry maybe I m not reading this correctly but I don’t understand this

Me too bluebelle

I'd keep writing to them, as often as you want to. Even if they don't reply, they'll know you wrote. Good luck OP.

Keep writing to them. Good luck !

I am a bit puzzled. Possibly they joined the military to get away from home as well and see you in some way as having been complicit in whatever nastiness they endured at home. I do not mean that you were complicit in any way, but young men in their 20s, and in the military can be very black and white in their judgments.

I would keep in touch lightly, birthday and Christmas cards with letters. Give it a couple of years, their views will change and they will judge very recent events calmly and come to other conclusions.

I would continue writing and keeping in touch as you know in your heart of hearts they was brainwashed into thinking/saying things about you which they didn’t really believe. I would also write heart felt letters to each of them leaving them so even if they don’t read any before they will read when anything happens to you and they will know you always wanted them in your life

I would not give up on thinking you will never see your Grandsons again. There Father will be found out at some point.... Their Father is what he is and your Grandsons have to find out the hard way. I would send them a heartfelt letter, remember their Birthdays & Christmas and give them the time to work matters out for themselves. It is so difficult when people tell lies about you and upsetting. One day they will be in touch...in the meantime you have to try and get on with your own lives...you know how good you where to those boys now men and they have to realise that. x

I agree with everyone who has said to keep on doing what you're doing Hope. There may come a time when they'll listen to their mum and will realise that whatever their father has told them about you is untrue.

I hope your daughter does leaves this awful man and will be able to find peace and happiness in a life without him and that one day you'll be a family again with your GS's.